The collection or preservation of biological cells in fluid suspension is common in medicine and biology for the purpose of detecting disease. For example, naturally voided urine contains urothelial cells from the lining of the bladder. If the urothelial cells are separated from the urine and then placed on a substrate surface, such as a microscope slide, examination of the cells can determine the presence or absence of certain diseases. Another example is the PAP Smear Test which involves the artificial exfoliation of epithelial cells from the cervix of the uterus and the subsequent suspension of the exfoliated epithelial cells in a water/alcohol solution to preserve and protect the cells. If the epithelial cells are separated from the solution and then deposited on a microscope slide, examination of the cells can determine the presence or absence of pre-cancerous lesions on the cervix.
However, current techniques for the preparation of specimens from cellular suspensions are deficient since the cellular suspensions may contain debris and contaminants which can interfere with the examination of the desired ("target") cells. For instance, in the case of cervical epithelial specimen samples, the contaminants may include leukocytes, erythrocytes, bacteria and mucus. In addition, the typical specimen sample may contain several layers of cells and/or the cells may overlap one another, thereby rendering the detection of cell abnormalities difficult. Another reason is that, for the Pap test or indeed any other type of test requiring an exfoliation instrument, the technique of transferring the collected cells from the exfoliation instrument to the glass slide can be very inefficient. In some studies it has been shown that less than 20% of the collected sample is effectively transferred. By contrast, a liquid-based specimen allows, as a preliminary step, all of the collected cells to be rinsed or washed off of the exfoliation instrument into the collection fluid thereby improving specimen recovery and aiding in subsequent diagnostic accuracy.
With the exception of a membrane filter tube, all components used in the preparation of a biological specimen are reusable. This gives rise to the possibility of sample-to-sample contamination which in the context of medical applications cannot be ignored.
Accordingly, there remains a need for an apparatus and method for preparing specimens from cellular suspensions which enhances the ease and accuracy of evaluation of biological cells for abnormalities, and which eliminates the potential for sample-to-sample contamination.